In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art.
Stamping techniques include graphic transfer, embossing, forming, cutting, and the transfer of materials onto or into a substrate, such as with hot stamping for transfer of patterns of foils and the deposition of chemical or biochemical reagents by contact printing, for example the deposition of inks and biological sensor molecules. Stamping processes typically replicate a pattern into, onto, or through, a substrate by the application of a patterned tool.
Embossing is a technique in which a stamping tool is pressed into a substrate, and causes material around the tool to shift and form a replicated structure in the substrate. The replicated structure produced is a negative image of the embossing tool. Forming is a similar technique to embossing and usually performed on substrates that are thinner than the structure to be patterned, a common example is that of blister packaging. Die cutting also involves the application of a patterned tool, however it typically cuts partially or wholly through the substrate around the pattern outline of the tool. The hot foil stamping method can be used to transfer a thin film, such as a metallic or graphic layer, from a carrier layer onto a substrate. The process usually involves bonding of the deposited layer onto the substrate by temperature and pressure, which also induces release of a coating from the carrier tape. Stamping foil is often used in processes which involve deposition of metallic layers for decorative coatings. Such metallic layers are typically produced on carrier tapes, such as polyester, with a wax release that melts at the stamping temperature. Similarly, the contact printing process transfers a material, often in the form of a liquid, from the stamping tool onto the substrate surface.
Prior art devices and methods for the stamping of materials typically involve the use of a specifically patterned tool that is used to form an entire patterned structure or area. An example is in microoptics and microfluidics in which a tool is made to replicate the entire desired pattern. The limitation with this approach is that an entirely different tool is required for each different pattern that is needed.
In some stamping situations such as embossing, the quality of replication is dependent on factors such as time, pressure, and temperature. Consequently, the size of the pattern to be replicated is limited by the processing machine's capabilities. As the size of the pattern to be replicated increases so do the force and dwell time required to shift the material from the replicated area. For larger structures this becomes more difficult as the material shifted when embossed is required to flow to other regions within the bulk material. Problems of material relaxation and stress after the embossing process can cause the replicated structures to deform.
Development of embossing processes for forming microfluidic structures started in the late 1990's using imprinting or stamping processes. High aspect ratios are often required to form such structures. A hot embossing process was developed to help structure replication and is commonly used in the research environment, as described in: Becker et al., “Polymer microfabrication methods for microfluidic analytical applications”, Electrophoresis 2000, volume 21, pages 12-26; Becker et al., “Polymer microfluidic devices”, Talanta 2002, pages 267-287; and Heckele et al., “Review of on micro molding of thermoplastic polymers,”, J. Micromech. Microeng. 2004, Volume 14, Number 3, pages R1-R14. The hot embossing process is a subset of the standard embossing process except that the temperature of operation is typically close to the material's glass transition temperature and the embossing pressures are lower. As with all embossing techniques, the quality of the replicated structures is dependent on several parameters including imprinting pressure, temperature, time and material properties. A problem with this technique is the difficulty and time required for temperature cycling to achieve the high aspect ratio structures, and the tendency for larger structures to trap air bubbles. Furthermore, there are limited materials suitable for this process, which in turn limits the number of materials available with suitable bulk and surface properties for product applications.
High-throughput production techniques that have been developed typically involve the use of reel-to-reel production systems for part fabrication of films. Examples of these include British Patent Application No. 9623185.7, which describes a UV curing process evolved from the optics industry for microstructuring films. The process works by coating the substrate with a thin UV-curable resin, then using a master template to emboss the pattern and cure the resin during contact with the template. U.S. Pat. No. 6,375,871 describes an extrusion process onto a film followed by roller embossing of the laminate or resin on the web. U.S. Pat. No. 6,375,776 describes a forming tool for use on a web system for microstructuring films. The main limitations with these techniques are that: they are limited to relatively thin substrates, or films, for operation on a web; have limited materials available that are suitable for this process, which in turn limits the number of materials available with suitable bulk and surface properties for product applications; require separate relatively expensive tooling for each pattern; and there are generally long setup delays associated with tooling changes.
The formation of conductive circuits on a substrate is usually performed via etching, screen printing, or electroplating processes. All of which are relatively expensive for small production runs due to the associated tooling and operational costs. Milling of electroplated substrates is a well-known alternative for rapid prototyping but is limited in dimensional capabilities and requires planar substrates, of which there are few commercially available materials.
Contact printing has been commonly used for the patterning of small quantities of liquids onto a surface. These liquids include inks and other chemicals or biological reagents for applications such as: information encoding, as with text; decorative or protective coatings; altered surface properties for wetting and bonding, including hydrophilicity, permeability, surface energy, and altering the molecular surface; and the deposition of reagents for sensor or actuator fabrication.
A main disadvantage with all of these production techniques is the time and cost associated with setting up the tooling required for a new pattern, and the operational cost for small production runs. With larger production runs these costs can be amortised over the number of parts fabricated, but for small production runs the individual part cost becomes prohibitively expensive.
Furthermore larger structures are problematic to stamp without substantially modifying existing equipment, and process dwell times are often increased with the size of the structure.
Thus, there is a need in the art for low cost arrangements and methods for stamping of individual parts or small production runs with different patterns, without requiring pattern-specific tooling. There is also a need for tooling arrangements and methods capable of producing larger patterned areas without increasing the size, cost, or complexity of existing machinery.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.